R-iLACCO1.1 is a genetically-encoded sensor for lactate. It contains the L-lactate binding domain (LBD) of the Escherichia coli lldR gene (without the DNA-binding domain), into which a circularly permuted red fluorescent protein (cpmApple) has been inserted at position 109. A number of amino acid substitutions have been introduced into the cpmApple and lldR-LBD coding sequences by directed evolution (PMID:37891202).